Part II

8-speed Automatic Gearbox 8HP

Driving situation evaluation

Winter program
The winter program is activated/deactivated automatically. A defensive shift characteristics and shift stabilization are provided on the basis of the respective basic map (avoiding pendulum shifts). This enables the highest possible stability and driving safety on winterly, icy roadways. Stable gear positions support running gear interventions of automatic stability control (ASC) or dynamic stability control (DSC) in an optimum way. Downshift requests that result in tensile force and could lead to spinning wheels are suppressed. This exempts downshift requests explicitly requested by the driver. As long as the winter program is active, functions that influence the stability of the vehicle are only effective to an extent where instability is avoided or they are completely switched off.

Hill and trailer function
The hill and trailer function adapts the shift strategy to higher tractive power requirements. The corresponding tractive power reserves are built up and, depending on the engine performance available, engine speed level is increased. This excludes or limits the tendency for pendulum shifts and unnecessary frequent gear changes during driving. One driving resistance sensor constantly establishes deviations of the current driving resistance with relation to a reference value stored in the control unit. Vehicle parameters are, for example vehicle weight, gearbox, axle transmission ratio, rolling resistance and drag. The reduced performance of the engine in higher altitudes (approx. 1 % loss of filling per 100 meters) is adapted with hill adaptation. If possible, the loss of filling is compensated using the engine speed. The correction is calculated with a relation value from the determined air pressure and a reference value stored in the control unit.

Corner function
The corner function serves to support the dynamics driving experience. In addition, the corner function protects against gearshifts that would overstress the force application potential of the wheels. When cornering with a corresponding lateral acceleration, the driver gets the feeling that the performance of the engine is supplied sufficiently. Upshifts are partially suppressed with regard to driving safety and comfort. On a road with several corners (constant change of lateral acceleration) the corner function is not deactivated on straight stretches in-between. Upshift suppression remains on when going into the following corners. For comfort reasons, gears are not maintained at high engine speeds in long corners.

Braking downshift function
Depending on the performed braking action, downshifts are triggered at different speeds and only for as long as the driver is braking. For this reason, vehicle deceleration is determined by a change of the speed-proportional signal (wheel speed or gearbox output speed) or using the brake pressure in the wheel brake system. The optimum shift speed is determined depending on the following values for the individual downshifts from one or several stored characteristic curves:
- Speed when starting to brake
- Determined deceleration or read brake pressure

Control function for speed
Speed-controlled driving mode is supported by the shift strategy to achieve an efficient and smooth overall behavior. It ensures that the acceleration or tensile force (uphill driving) requested by cruise control is reached.
Additionally, there is no loss of comfort by increased gearshift activity or pendulum shifts. In line with the driving situation (constant-speed driving, acceleration, deceleration), cruise control selects the requested tensile force and the ideal gear. When cruise control is active Integrated Chassis Management (ICM) takes over the dynamic vehicle management task. Within certain limits the driver does not have to interact and the system actuates engine and service brake. For this purpose, Integrated Chassis Management (ICM) calculates the desired acceleration and transmits it. Digital Engine Electronics (DME) and Digital Engine Electronics 2 (DME2) determine the required engine torque on the basis of the current driveline transmission. This request is implemented within physical boundaries. It additionally provides a corresponding virtual accelerator pedal value. Amongst others, Integrated Chassis Management (ICM) detects the following operating conditions:
- Control function for driving at constant speeds
- Control function for the following operation
- Sensing any set speeds
- Corner control function
- Control function on downhill gradients

These operating conditions must be supported by the gearbox with individually adapted shift strategies. This corresponds to the features of the controller and also to subjective driver choices with relation to the shift characteristics. The gear selection mechanism uses suitable shift diagrams. The difference is that the torque or load request to the gearbox comes from the Integrated Chassis Management (ICM). Gear selection achieves that the selected speed is set without any loss of comfort (no increased shift activity or pendulum shifts). Similar to driver mode, the automatic transmission supports in the following driving situations:
- Normal operation with emphasis on comfortable shift characteristics and best-possible efficiency
- Uphill driving and trailer towing with the required tensile force reserves to avoid unnecessary shifting activity
- Downhill driving with downshifts that support deceleration
- Cornering detection with reduced shift activity to support the specific ACC control characteristics

Required gear determination
A special required gear determination is used in the 8-speed automatic gearbox. During downshifts it enables faster engagement of the matching gear for faster acceleration. For this purpose, the required gear is calculated from the speed with which the accelerator pedal is depressed. As soon as the driver starts depressing the accelerator pedal, speed is evaluated and the matching required gear is calculated for the downshift. The required gear is then directly engaged, possibly even by shifting down across several gears.

Characteristics curve of shift speeds
The electronic transmission control is equipped with three different shift speed levels.
The higher the level, the faster the gearshift. The corresponding shift speed levels are engaged depending on the selected driving programs and the speed at which the accelerator pedal is depressed.

Notes for Service department

Automatic transmission fluid
The 8-speed automatic gearbox is equipped with a life-time oil filling. During the entire running time the 8-speed automatic gearbox does not require an oil change.
The approved life-time oil type must be used after repairs on the gearbox or transmission oil cooler.

NOTICE: Do not mix with other automatic transmission fluids.

The life-time oil type must not be confused or mixed with other automatic transmission fluids. Using other oil types could result in a gearbox failure.
Use Shell L 12108 automatic transmission fluid.

General notes
We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.